1. Field of the Invention
The present invention relates to an evaporated fuel control system to keep the fuel tank internal pressure within a specified range and thereby prevent the evaporated fuel in the fuel tank from leaking out into the external atmosphere.
2. Description of the Prior Art
The fuel tank conventionally available is shown in FIG. 17. The fuel tank 68 has a filler pipe 67 inserted therein which is bent at 69 to hold the fuel, so that the liquid fuel contained at the bent portion 69 prevents the evaporated fuel in the tank 68 from getting out into the open air. With the structure of the fuel tank 68, however, there is a problem that opening the filler cap when the tank 68 is filled with fuel to its capacity or close to the capacity may result in the fuel flowing out through the filler pipe 67, which is undesirable in the light of safety and environmental pollution.
Generally, the object of the evaporator system is to keep the internal pressure of the fuel tank within a specified range, prevent deformation and damage to the fuel tank and therefore fuel leakage and at the same time to prevent the fuel vapor in the tank from getting out and polluting the environment. To explain in more concrete terms, a part of the fuel in the tank usually evaporates and this raises the internal pressure. But, if the tank is not provided with an evaporator system, this increase in pressure will continue until the fuel tank is deformed and damaged leading to a serious problem such as fuel leakage. Also when the temperature in the fuel tank falls, the internal pressure becomes negative, which may result in deformation of the tank. To prevent such an accident, the fuel tank is required to communicate with the outside air to minimize the internal pressure rise or fall in the tank. But the provision of a vent hole only is not satisfactory and there is a possibility of the tank being filled up to more than the normal capacity during filling because the evaporated fuel in the tank flows out through the vent hole even after the breather is submerged in the fuel. This poses a threat to safety. Furthermore, the evaporated fuel in the tank will continue to be released into the open air until there is no fuel remaining in the tank, polluting the environment to cause public pollution. This is not desirable also from the energy conservation point of view.
To solve these problems, vehicles are equipped with the an evaporator system such as shown in FIGS. 18 and 19. The conventional evaporator system will now be explained by referring to FIGS. 18 and 19. The evaporated fuel in the fuel tank 105 is led to the canister 99 through the evaporator line 108 in which is provided a check valve 109 that opens only when the difference between the pressures before and after the check valve exceeds a specified value. The action of the check valve prevents the unlimited flow of the evaporated fuel from the tank 105 into the canister 99, so that the canister will not become saturated by the larger inflow of the evaporated fuel than it can adsorb, thus preventing the raw gas from dripping from the drain 58. The check valve 109 also has another function. When the filler gun 21 is inserted into the filler pipe 107 after removing the filler cap 106 from the filler pipe 107 and when the inlet of the breather pipe 98 attached to the filler pipe 107 is submerged below the liquid surface, there is no way out for the evaporated fuel in the tank 105 and this makes the fuel loading difficult. In that case, the check valve 109 prevents the excess loading of fuel into the tank. In this way, the check valve 109 controls the amount of vapor passing therethrough and the vapor is further led to the canister 99 where it is adsorbed by the active carbon 59. The canister 99 adsorbs not only the evaporated fuel from the fuel tank 105 but also the evaporated fuel generated in the float bowl 62 of the carburetor 61. When the engine is started, the evaporated fuel adsorbed and held in the canister 99 is introduced through the purge line 63 into the combustion chamber, to be burnt, together with the fresh air drawn in from the drain 58 by the negative pressure generated by suction when the throttle valve 60 is opened. The opening and closing of the purge line 63 is controlled by the diaphragm 65 of the canister 99 which in turn is opened and closed by the negative suction pressure supplied through the vacuum line 64.
As explained above, the evaporator system currently employed in automobiles keeps the evaporated fuel generated in the fuel tank 105 and carburetor 61 from getting out into the atmosphere and also maintains the internal pressure in the fuel tank 105 with in the safe range. In the figures, reference numeral 106 denotes a filler cap. It should be noted, however, that this evaporator system releases the evaporated fuel almost without restriction during fuel filling, as shown by the arrow B. To put it in numerical terms, when gasoline is poured into the tank from the filler gun 21 in the amount equal to a volume V, there is the following relation since the air contained in the tank 105 is kept at the atmospheric pressure: V=V1+V2+V3, where V1 denotes the evaporated fuel released from the filler pipe 107, V2 represents the vapor fuel released through the breather pipe 98, and V3 represents the vapor fuel released through the evaporator line 108. Since the check valve 109 is provided in the evaporator line 63, V3 is almost zero. That is, V is almost equal to V1+V2. In other words, the amount of gasoline supplied V is almost equal to the vapor fuel V4 released from the fuel injection port. This means that when gasoline is supplied into the tank at a rate of 40 liters per minute, nearly 40 liters of gasoline will find its way out into the open atmosphere every minute. This will present a serious problem when a restriction on the vapor fuel discharge during fuel filling is legislated. The evaporator systems used on the current automotive vehicles are fundamentally the same although there are small variations in the structure of the check valve 109 and canister 99, and they all have the above-mentioned problems.
The Japanese Patent Laid-Open No. 164763/1980 is cited as an example of an evaporated fuel discharge prevention device for the internal combustion engines of automobiles. We will explain about this device by referring to FIG. 20. FIG. 20 shows the evaporated fuel discharge prevention device for internal combustion engines of automobiles which is installed in a passage through which the evaporated fuel is discharged into the open air. The vapor fuel discharge prevention device has a canister 71 containing the adsorbent 72 by which the vapor fuel introduced from the vapor fuel inlet port is temporarily adsorbed while it is moving toward the open air communication port 73. When the internal combustion engine is run, the adsorbent 72 is cleaned by fresh air introduced from the open air communication port 73 and the vapor fuel removed from the adsorbent 72 is discharged from the canister 71 through the vapor fuel discharge port into the engine.
The device also has another canister 80 which contains adsorbent 87 and which is divided in two by a separator 84 except at the bottom. Formed at the upper part of one divided part of the canister 80 are a vapor fuel inlet port 85 and a vapor fuel discharge port 86. At the upper part of the other divided part of the canister 80 is formed an open air communication port 82. The vapor fuel inlet port 85 is connected to the upper part of the paper separator 88 by a pipe 78 through a solenoid valve 77. The pipe 78 is greater in inner diameter than the pipe 89 which connects the paper separator 88 and the canister 71. A suction pump 83 is connected to the open air communication port 82 through a three-way solenoid valve 79 which is connected at one end to the deadsorbing air inlet pipe 81. A solenoid valve 77 is operated according to the open-closed state of the cap 76 on the fuel injection port 75 in such a way as to open the pipe 78 when the cap 76 is removed. The three-way solenoid valve 79 also is operated according to the state of the cap 76 on the fuel injection port 75 in such a way as to communicate the open air communication port 82 of the canister 80 with the deadsorbing air inlet pipe 81 when the cap 76 is on the fuel injection port 75 and to communicate the open air communication port 82 with the suction pump 83 when the cap 76 is removed and the fuel injection port 75 is open. It should be noted, however, that the above evaporated fuel discharge prevention device has no purge control valve in the purge line, so that the purge line is open at all times degrading the exhaust gas. Furthermore, the device has no control valve for checking the full-tank level, so that the full-tank level is not clearly identified, which is dangerous. The further disadvantages of the device are that the structure of the device is complex and costly and that the negative pressure generating device is not sufficiently durable.
Still another example of the evaporated fuel discharge prevention device is disclosed in the Japanese Utility Model Laid-Open No. 67237/1986. This device is explained by referring to FIG. 21. The device has a valve mechanism installed in the fuel injection portion 90 of the fuel tank. The valve mechanism, when the fuel supply nozzle is inserted and hermetically sealed into the fuel injection portion 90, communicates the fuel tank with the active carbon canister for vapor fuel adsorption through the vapor passages 93, 94. The vapor fuel is recovered from the active carbon canister into the suction manifold. In more detail, the evaporated fuel discharge prevention device has the fuel injection portion 90 divided into a valve chamber 91 and a fuel supply nozzle insertion passage 92. The valve chamber 91 has one end of a vapor fuel passage 93 inserted therein. The valve mechanism consists of a valve element 96 urged by the spring 95 to partly project into the insertion passage 92; and a valve disc 97 which is linked with the valve element 96 and adapted to close the inlet port of the vapor fuel passage 93 that opens into the valve chamber 91. The above evaporated fuel discharge prevention device, however, has no purge control valve in the purge line, which means that the purge line is always open degrading the quality of the exhaust gas. This also presents a risk of compounding the situation in the event of an accident. The device also has a problem with respect to the durability and reliability of the filler seal.
An air cleaner for automotive engine is disclosed in the Japanese Utility Model Laid-Open No. 23486/1980. This is briefly explained by referring to FIG. 22. In the air cleaner 100 installed in the air suction system of the engine, a cleaner element 103 divides the air cleaner 100 into the dust side on the side of the air intake port 101 and the clean side on the side of the carburetor. On the clean side of the cleaner element is formed a layer of adsorbing material 102 to which the vapor fuel in the fuel tank 104 is introduced.
The automotive fuel tank disclosed by the Japanese Utility Model Laid-Open No. 23486/1980 has a fuel passage formed in the fuel filling pipe which, however, is not capable of preventing the vapor fuel from flowing out to the external environment. The evaporated fuel discharge prevention device incorporated in the gasoline tank supply port for the automobiles disclosed by the Japanese Utility Model Laid-Open No. 133521/1979 has a vapor discharge prevention cover which, however, is not good enough as a sealing structure and may not be able to seal the vapor depending on the shape of the filler gun.